Cans that can be easily opened without the aid of tools are very popular for packaging foods and beverages. Such cans feature a ring-pull top that can be pulled open along a notch in the material of the can by means of a manually operable tab. A beverage can of metal with a ring-pull top that can be pulled open along a notch line by means of a pull-tab is known, e.g., from EP 0 381 888-A.
Such cans with a ring-pull top are usually produced from either aluminum sheets or a steel sheet that is provided with a corrosion-resistant protective layer. Due to the lower costs, coated steel sheets have certain advantages over aluminum. However, it was determined that ring-pull tops of sheet steel require a higher force for tearing off the ring-pull top than ring-pull tops of aluminum.
DE 35 12 687 C2 discloses a method for producing steel sheets for easily openable can tops, by means of which a ring-pull top can be produced that makes it possible to easily open the can without excessively reducing the remaining metal wall thickness in the region of the notch. For this purpose, DE 35 12 687 C2 proposes to use a steel with a carbon content in the range between 0.01 wt % and 0.051 wt % and the alloying constituents silicon in an amount between 0.01 and 0.02 wt %, manganese in an amount between 0.32 and 0.35 wt %, phosphorus in an amount between 0.018 and 0.022 wt % and aluminum in an amount between 0.07 and 0.09 wt %. The steel is initially hot-rolled, then annealed after a cold-rolling step and subsequently subjected to a second cold-rolling step. After the cold-rolling, the steels are cleaned, tin-plated in a molten tin bath and subsequently finished for the production of a ring-pull top.
Other methods for producing ring-pull tops from steel sheets are known from DE 20 10 631 and DE 42 40 373 A1, wherein lines for a plurality of ring-pull tops are initially scored on a steel plate or a steel strip, and wherein the pre-scored plate or the pre-scored strip is then coated with a protective layer and the ring-pull tops are subsequently stamped out. A coat of lacquer or tin plating or chromium plating of the steel sheet, or even a plastic film that is laminated onto the plate or the strip as proposed in DE 42 40 373 A1, may be considered as protective layer. The protective layer may be applied onto one or both sides and provides the steel strip or steel sheet with a high corrosion stability such that cans produced from it can also be used for packaging aggressive foods or beverages.